B. Chaudret and R. Poilblanc, Organometallics, 1985, 4, 1722-1726 report the synthesis and characterization of a ruthenium complex, RuH.sub.6 (PCy.sub.3).sub.2. This complex was later formulated as RuH.sub.2 (H.sub.2).sub.2 (PCy.sub.3).sub.2 by T. Arliguie et al., Inorg. Chem., 1988, Vol. 27, 598-599. The complex was prepared from Ru(COD)(COT). (COD is 1,5-cyclooctadiene, COT is 1,3,5-cyclooctatriene and Cy is cyclohexyl.)
B. Chaudret et al., J. Am. Chem. Soc., 1991, 113, 2314-2316, report the synthesis and characterization of a ruthenium complex RuHX(H.sub.2)(PCy.sub.3).sub.2, where X is iodine or chlorine. The complexes were prepared from RuH.sub.2 (H.sub.2).sub.2 (PCy.sub.3).sub.2.
A. M. Joshi et al., Prog in Catal., 1992, 73, 143 describes nitrile hydrogenations using di- and tri- nuclear Ru(II) complexes containing chelating diphosphines such as 1,4-bis(diphenylphosphino)butane (dppb). They disclose a preference for [RuHCl(dppb)].sub.3 for nitrite hydrogenations.
U.S. Pat. No. 3,454,644 describes hydrogenations using L.sub.n MZ.sub.2, where n=3 or 4; M is ruthenium or osmium; L is independently PR.sub.3 or CO, preferably at least three being PR.sub.3 ; and the Z ligands being Cl, Br, or H. Specifically mentioned are RuHCl(PPh.sub.3).sub.3 and RuH.sub.2 (PPh.sub.2 Me).sub.4.
T. Arliguie et al., Organometallics, 1991, 10, 1888, disclose a structure for a compound in which dehydrogenation of a cyclohexyl ligand has apparently occurred. This structure is for a cationic (as opposed to neutral) species as indicated below. ##STR1## X-ray crystallography shows that one cyclohexyl group has been dehydrogenated, with removal of two H atoms, to a cyclohexenyl group, which is coordinated to the Ru center as an olefin ligand and by an agostic C-H-Ru interaction involving one of the allylic hydrogens.